Double oxides of yttrium and tungsten



March 23, 1965 H. J. BORCHARDT 3,174,822

DOUBLE QXIDES OF YTTRIUM AND TUNGSTEN Filed Feb. 14. 1961 PHASE :II

HOLE Y0 W03 PHASE I '0 c o B O O c c c o c 0 UMVUJJHJI INVENTOR HANS J. BORCHARDT AT BY 596* ATORNEY States This invention relates to a new class of oxide compositions. More particularly, this invention relates to double oxide compounds of yttrium oxide and tungstic oxide.

Oxides as a class are the most important high temperature materials now available and promise to retain this position because of their stability in oxidizing atmospheres.

Therefore, it is an object of this invention to provide entirely new double oxide compositions with useful properties. It is a further object of the invention to provide novel double oxide compositions which are the reaction products of yttrium oxide and tungstic oxide. Other and additional objects will become apparent from a consideration of the following detailed description.

These objects are accomplished in accordance with this invention which provides as a new composition of matter, a double oxide compound selected from the group consisting of YgOg, Y203, 4WO39Y203 and 8WO3'15Y203- The process leading to these novel compounds employs standard ceramic techniques and simply involves contacting an intimate mixture of the powdered oxides of yttrium and tungsten in appropriate concentrations, pressing said oxide mixtures into a desired shape, and heating said masses in air at atmospheric pressures at elevated temperatures.

The term double oxide compound is used herein to designate the composition of this invention which conforms to the formula WO -xY O wherein x may be one of the numbers 1/3, 1, 15/8, 9/4 and 3. It is used herein to denote the compound composed of yttrium oxide and tungstic oxide radicals.

It will be understood that instead of adding the oxides as such, chemically equivalent amounts of compounds of the metals concerned may be added. These are then converted to the oxides during heating to the firing temperature. Such compounds may be organic or inorganic. Examples in the case of yttrium are yttrium carbonate, yttrium oxalate, yttrium hydroxide and the like and in the case of tungsten, tungstic acid, ammonium tungstate, organic derivatives of tungstic acids, etc. The two oxides, or compounds liberating the same, are intimately mixed by any of the methods known to the ceramic art. The materials of the mixture are preferably both in a finely divided state, and dry mixing is preferred over wet mixing. To the mixture of the oxides, a suitable binder, usually in a solvent, is added in an amount sufiicient to allow the mixture to be cast or pressed into the desired shape. Binders suitable for this purpose are well known and include solutions of Waxy materials such as parafiin, solutions of stearic acid, camphor, starch and the like. A solution of parafiin in petroleum ether has been found satisfactory for this purpose. The binder remains during the pressing technique but escapes during firing.

The preparative procedure utilizes tungstic oxide and yttrium oxide or the equivalent compounds in essentially stoichiometric quantities as determined by the molar ratios of the oxides in each of the compositions. This represents preferred operating procedure, providing each product in essentially pure form. However, it can be seen from data summarized in Table I that each phase forms over a range of compositions. For instance, the compound, 3WO -Y O forms as a product in mixtures containing from about 2.4 to 49 mole percent yttrium oxide. in the lower concentration, i.e., up to about 25 mole percent yttrium oxide, the compound occurs with tungstic oxide. Stoichiometric mixtures provide the pure compound, whereas in starting mixtures containing excess yttrium oxide, the compound occurs with a new phase, WO -Y O The concentrations over which the compound, WG -Y O forms range from about 25.3 to 64.3 mole percent yttrium oxide. Starting mixtures containing from about 51.3 to 68.8 mole percent yttrium oxide yield the compound 8WG -15Y O those containing about 65.6 to 70.1 mole percent yttrium oxide, the 4WO '9Y O and those containing about to 98 mole percent yttrium oxide, the compound VVO -3Y O In each instance, stoichiometric mixtures provide the pure phase and those which deviate appreciably from stoichiometry, a mixture of two phases.

TABLE I Firing Temperature C.)

Mole Percent YQOS W-Y Ratio Product I l-II. 1+1r. IT

liq-III. II+III. III

l l ammer These data, together with additional data obtained from high temperature studies of intermediate compositions, are tabulated graphically in FIGURE 1. This represents a pseudobinary temperature-composition diagram for the system tungstic oxide-yttrium oxide. The compounds are represented by lines rather than by areas, reflecting the fact that no evidence for homogeneity ranges can be obtained by X-ray difiraction procedures.

Purely for practical reasons, the firing step is carried out at temperatures between about 900 and 1400" C., depending to a certain extent upon the composition of the starting mixture. Generally, samples containing more than 25 mole percent yttrium oxide are heated at 1400 C. and those containing less yttrium oxide at 1100 C. The use of 1100 C. in the latter instance is chosen only to avoid the presence of a liquid phase in the course of the reaction, a eutectic being formed in this range between W0 and 3WO -Y O which melts at about -1155 C. However, the presence of the liquid phase represents an inconvenience-not a limitation-and does not impair the formation of the compound 3WO -Y O Therefore, the higher synthesis temperatures may be employed if desired. The above stated temperatures are the most satisfactory from a process point of view, since the compounds form in reasonable periods of time and since the systems under these conditions appear to represent equilibrium situations. However, the phases are seen to form at both higher and lower temperatures. For example,

may be prepared from a stoichiometric mixture by heating at 750 C. for 22 hours or at 900 C. for 30- minutes; WO -Y O is detected in a stoichiometric mixture after heating at 1100 C. for 24 hours, although the transition is complete only after one week at this temperature; 8WO -15Y O is formed from a stoichiometric mixture by heating at 1100 C. for 24 hours; and any of the compounds 8WO l5Y O 4W0 -9Y O and WO -3Y O may .be obtained by firing mixtures containing stoichiometric proportions of the respective oxides at 1700 C. for less than 2 hours.

The method of preparation will be illustrated with a specific example which is typical of the method for preparing any of the materials of the present invention, yet is not intended to limit the same. The example deals with the preparation of the compound WO -Y O Example I Yttrium oxide (0.9129 part by weight, particle size approximately 2;]. as measured in a Fischer subsieve sizer) and 1.000 part by Weight of tungstic oxide (particle size approximately 8 1) are mixed dry on a vibrating mixer for approximately 3 minutes. A paste is made by adding a 0.5% solution of parafiin in petroleum ether, and the mixture is pressed into the form of a pellet in a die. The pellet is slowly heated in air in platinum to 300-400 C. at a rate of about 20 C. per minute to allow the binder to burn off slowly, and then the temperature is increased to 1000 C. for 1 hour. Heating at this temperature irnparts green strength. The pellet is then transferred to a silicon carbide resistance furnace Where heating in air is continued at 1400 C. for 4 hours. X-ray examination indicates the presence of only one phase, WO -Y O To characterize the compounds of this invention and to establish at which compositions single phases form, X- ray powder dififraction techniques have been utilized, and those skilled in the art will be aware of the limitations therein. It is recognized, for instance, that X-ray powder patterns may not reveal the presence of a phase unless about five percent of that phase is present. Because the stoichiometric formula of each phase herein described has been established by the molar ratios of the oxides yielding only one phase as detected by powder diffraction, it is possible, although not likel that the stated formulae may deviate by an amount consistent with this limitation and should be so interpreted.

The new binary oxides of this invention are white, crystalline substances, having crystal structures substantially difierent from either of the oxide components. They appear to be thermodynamically stable at their temperature of formation, forming spontaneously from their parent 0xides, and there is no indication of any structural changes even after the compounds have been heated for at least a week at 1400 C. X-ray powder patterns of each of these phases which serve for their characterization are given in Tables 11, III, IV, V and VI. It appears that, unlike the others, the compound WO -3Y O undergoes a phase transformation between 1400 C. and its melting point. The X-ray pattern obtained when this compound is solidified from its melt is not that of the original compound, of yttrium oxide or of any other previously encountered phase. The pattern contains very few lines and can be indexed on the basis of a face-centered cubic unit cell. The most likely explanation is that this is a frozen-in high temperature phase of WO -3Y O 4 TABLE II X-RAY DIFFRAOTION DATA [Phase I (W:Y=3:2)]

Line No. 20* d n 13.1 6. 75 60 14. 2 6. 23 30 18. 7 4. 74 30 19. 2 4. 62 5 20.3 4. 37 60 20.9 4. 25 3O 21. 2 4.19 40 21. b 4. 11 100 21.9 4. 06 80 23. 3 3. S1 30 23. 7 3. 75 55 23. 9 3. 72 55 25. 4 3. 50 70 26. 4 3. 37 70 28.2 3. 16 50 28. 6 3.12 50 30. 9 2. 89 40 31. 7 2. 82 40 37. 3 2. 41 20 44.0 2. 056 20 44. 8 2.021 20 *CuKa radiation.

TABLE I11 X-RAY DIFFRACTION DATA [Phase II (W:Y=1:2)]

Line No. 26* d I/I 1.7. 55 5. 05 20 18. 54 4. 78 20 20. 57 4. 31 2 20.99 4. 23 22. 50 3. 95 15 23. 28 3. 83 15 24. 2a 3. 66 28. 10 3. 17 2 28. 9S 3. O8 90 29. 55 3.02 100 32. 22 2. 77 10 32. 55 2. 75 25 33. 60 2. 66 25 34. 2. 61 10 35. 5o 2. 52 20 36.15 2. 48 2 38. 15 2. 36 5 41. 40 2.1. 9 2 41. 95 2. 151 10 42. 40 2. 130 10 43. 35 2.085 2 44.05 2. 054 2 44. 2.032 5 45. 45 1. 994 5 45.85 1. 977 5 47.45 1. 914 20 48.15 1. 888 15 49.15 1.852 5 49. 1. 833 40 '50. 20 1. 816 2 51. 3 1. 779 10 52. 15 1. 752 2 52. 1. 734 10 54. 15 1. 692 5 54. 50 1. 682 5 *CuKa radiation. N orE.-L1nes 16-35 appear to be closely spaced double lines.

TABLE IV X-RAY DIFFRACIION DATA [Phase III (W;Y=1:3.75)]

Line No. 20* d 1/1 *CuKa radiation.

C., the measured rate of volatilization of the mixed oxide is 1.l:0.1 l0 g./sec. cm. Whereas the tungstic oxide volatilization, measured under the same set of con- Tungstic oxide is essentially stabilized with respect to volatilization by forming this mixed oxide.

The

ditions, is 4.7i0.2 g./sec. cm.

This mixed oxide is useful as a ceramic coating material especially applied over substrates such as tungsten metal by flame spraying to improve their oxidative stability.

The compound WO -Y O is a White solid that melts incongruently at about 1700 C. The solid is luminescent upon exposure to short Wave length ultraviolet radiation, for example 2537 A. light, and to X-rays. luminescent oxide is useful as an X-ray detector and as luminescent screens. With specific regard cent oxide, WO -Y O it is to be understood that some luminescence Will appear as long as the Phase II, Table l and FIGURE 1) is present. As a mixture of the materia l of lhase I1 and any of the progresses in either direction from the pure WO -Y O composition, luminescence will, of course, be diluted in proportion to the amount of WO 'Y O which is actually present. 0

chardition of appropriate Pd 1 a i r e t s a 6 .m m m mm 3 m h u 0 a 11 2 h w S Y P i h a r x p 0 t am W o 0 5 0 5 1 1 2 4 1 u H I wmmmmmuommwmwmwwflmmwmm 6 &&3 &3 a&3 &3 2 .s 3 111111111 m A D m 06705n08352480700995623 A W O 1 2 n V C X E A M L R B m N A r m s a T n Y W. A a N X m D *CuKa radiation.

The W0 -Y TABLE VI X-RAY DIFFRACTION DATA is a new host lattice and, of course, the luminescent acteristics may be altered by the ad Each of the mixed oxide compositions, WO -3Y O ite, well-vitrified ceramic bodies which melt above 2200 C. and are useful Refractories can be prepared in a variety ping an appropriate mixture of the oxides and a binder and firing at about 180-0 C.

The above description has been given for clearness of understanding only and no unnecessary limitations are to be imposed thereby. It will be understood that variations and modifications can be effected within the spirit and scope of the invention as defined hereinabove and as defined in the appended claims.

1. A refractory double oxide selected from the group consisting of WO -3Y O 4WO -9Y O and 2. The double oxide compound Whose composition corresponds to the formula WO -3Y O 3. The double oxide compound Whose composition corresponds to the formula 4WO -9Y O 4. The double oxide compound whose composition corresponds to the formula 3WO -15Y O References Cited by the Examiner Gmelin-Krauts: Handbuch der Anorganisc Band VI, Ableilung 2 (1928-32), pa

S t n a e m s a e s O 6 n y 2 l e O b Y 4 m 5 y C S 11 t a m .1 .1 "l a I f I i 3 U 6 O C nu p Y :1 I W S f W i a o 8 0 0 5 0 3 4 4 5 2005250005250255005 n H I 187581323 789 rd d 2222L1LLLLLLLLLLLLLL 001815757061344135451069231367 atLahssL/xaoatl & 61 5 6 7 6 2 L X n W n V e S a u h W n M u m L CuKa radiation.

hen Chemie,

go 753. Hoffman: Lexicon der Anorganischen Verbindungen, Band 2, No. 56-81, page 748.

MAURICE A. BRINDISI, Primary Examiner.

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1. A REFRACTORY DOUBLE OXIDE SELECTED FROM THE GROUP CONSISTING OF WO3$3Y2O3, 4WO3$9Y2O3 AND 8WO3$15Y2O3. 